High temperature plasma arc melters are traditionally utilized for the production of irons and steels and for other extractive metallurgy purposes. Recent developments in the usage of plasma arc melters for the processing of minerals and waste material have generated a need for improved methods of removing molten basalt from the primary melting chamber.
Basaltic slags and reduced metals are produced from waste type arc furnaces at temperatures nominally in the range of 1500.degree. C. to 2000.degree. C. Basaltic slag are generally viscous in nature even at high temperatures and are very corrosive. The viscous nature of these slags presents difficulties in removal of the product from the melter. One standard method to aid in the removal is to add fluxing agents such as alkali metals Na, K etc.) or alkali earth metals (Ca, Mg, etc.) to chemically change the composition and reduce the viscosity for a given temperature range. However, it is often desirable to minimize the addition of fluxing agents to the melt for economic and product specification purposes.
Another method used is raising the temperature of the melt a sufficient amount to ensure a flowable liquid as the liquid progresses through an opening in the melter (removal means). Alternately, heat may be added to the removal means to ensure a flowable liquid stream. The temperature of the melt must be sufficient to provide a flowable fluid through the product removal means (taphole or weir) to remove a generally viscous product. Complications arise due to the fact that basaltic slags generally remain viscous above 1535.degree. C. (melting point of iron) and are very corrosive and acidic. The acidic nature of these slags often precludes the use of standard components generally used in the iron and steel industry which are commonly available.
Electrically fired plasma torches are currently used for the processing of minerals and waste material. These torches tend to operate in the 5,000.degree. C. to 10,000.degree. C. range at the torch with bath temperatures approaching greater than 2500.degree. C. in the hot areas. Graphite electrode plasma arc furnaces may be operated in very short arc or submerged orientations and tend to operate at slightly lower bath temperatures in the range of 1500.degree. C. to 2000.degree. C. Operations with higher bath temperatures provide the ability for greater control of viscosity, but result in energy and maintenance penalties. Operations with a bath temperature just high enough to encourage chemical reactions and the production of basaltic type material provide economic and maintenance advantages but complicate the removal of the basaltic slag product.
Molten material is generally removed from the furnaces by tipping the furnace and pouring the material over a spout, by opening a tap hole located in the side or bottom of the funiace, or by flowing the material under and over weir structures located at the bottom of the furnace. Eccentric bottom tapping is generally standard practice for tapping electric arc furnaces used in the production of steel. Molten material is generally removed from blast furnaces by drilling out a plug of material located in a hole through a sidewall in the furnace.
Typically, the molten material is removed in a batch operation in which nearly all of the molten material is drained from the furnace once the hole is tapped. In industrial use this method provides a relatively simple and inexpensive method for product removal. However, it is often desirable to start and stop the molten stream rather than dispense all of the molten material at one time. This requires opening, closing, and maintenance of the tap hole and difficult control of fugitive emissions from the hole. The hole is generally closed with a disposable plug, ram gun, ramming paste or mixture, or other type of mechanical closures. These closures are often difficult to install and remove and may be susceptible to leaks.
Therefore, there is currently a need for a tapping apparatus and method which creates a tap hole which can be repeatedly opened and closed, and a method for confining fumes generated when the tap hole is opened during the removal of the molten material from the furnace.